www.ntia.doc.gov for a downloadable PDF of the spectrum assignments in the U.S.
www.ero.dk for frequency spectrum assignments covering most of Europe
www.cept.org
www.fcc.gov to look up an FCC i.d. from the website to help you track down the true manufacturer of a Wi-Fi radio product, despite the label or brand

purchase pigtails online – not available in stores:
www.ecwest.com
www.fab-corp.com
www.hyperlinktech.com
www.wlanparts.com
www.ydi.com